Conventionally, a difference between two similar patterns has been extracted by a human visual check. More specifically, one of the patterns is set as a reference pattern, and the reference pattern and the other pattern are compared through the human eye, thereby extracting a difference.
In addition, common patterns (moving patterns) that are present at different positions in two similar patterns (overall patterns) are also extracted by a human visual check. More specifically, one of the patterns is set as a reference pattern, and the reference pattern and the other pattern are compared through the human eye, thereby extracting moving patterns.
A human visual check, however, can cope with only a case wherein a difference or moving pattern between two similar pattern is clear. That is, if overall patterns are complicated or a difference or moving pattern is small, it takes time to extract it, and an accurate check cannot be made. If a plurality of moving patterns are present, it is difficult to detect all the moving patterns.
It is an object of the present invention to provide a pattern extraction apparatus which can accurately extract a difference and moving pattern between similar patterns in a short period of time.